Living Shorelines Types from large to small Downsizing a Living - PowerPoint PPT Presentation

Living Shorelines Types from large to small

Downsizing a Living Shoreline; Retail-scale Options for Private Properties on Exposed, Rapidly-Eroding Coasts David d. McGehee, P.E., D.CE Emerald Ocean Engineering LLC and Taylor “Chips” Kirschenfeld Environmental Consultant

Project Location

Existing Conditions

Owner's Mission Reduce Upland/Shoreline Erosion Maintain Recreational Beach Be a Good Neighbor Utilize a Living Shoreline (“. . . like Project Greenshores”)

Average Erosion @ Project 1997 - 2013 ~ 2 ft/yr Over 1 ft/mo from 2008 - 2010

Site Analysis Calculated Net LST Potential (cu yd / yr)

LST potential shows accumulation: Why isn't the project accreting? No southern sediment supply If shorelines are retreating, where is all that eroded sand going? Offshore (see offshore profiles)

CONCEPTS

Design Challenges/Design Strategies Optimize reef bw performance to: Eliminate/reduce upland erosion & offshore transport Sill; dissipate high steep waves; pass low long waves Maintain the saltmarsh Average H s < H th (Douglas & Stout, 2004) Permit adequate longshore transport Salient good; tombolo bad; bobcat OK Adapt to sea level rise Rise with it: 1) maintenance {cheap}; 2) oysters {free} Survive extreme events Stay low; stay flat

Design profile

DESIGN PLAN

Voluntary Adaptive Management Plan 03/13/16

CONSTRUCTION

Cost Comparison For 155 ft of shoreline protection: Traditional Bulkhead - $40-60 K Living Shoreline – $ 70 K Offshore Emergent Breakwater > $100 K

State-mandated Monitoring 11 Profiles extending ~200' offshore 250' N & S of project bounds Neighborhood seminars Semi-annually, 3 yrs

1Week Post Construction

I Week Post Construction

1 Year Post Construction

1 Year Post Construction

Missions Accomplished ! (?) OWNER'S DESIGNER'S ● Reduce erosion ● Reduce erosion √ A ● Maintain saltmarsh ● Recreational beach √ A ● Allow LST ● Neighborly C ?? √√ ● Survive ● Living Shoreline √√√ Incomplete ● Adapt to SLR – Cheap A – Free D

LESSONS ● Saltmarsh vegetation can thrive on exposed bay shorelines ● Submerged Reef BW perform well in X-shore dominated shorelines ● Submerged reef BW can be: – Reef habitat as valuable as marsh – Breakwaters as effective as emergent bw

??Questions?? Low tide visitor ↑ High tide visitor →

Offshore Profiles => Offshore Trx. 15 yrs upland erosion ~ Vol. > P0

Profile 4S – Local Effects (LST-o-meter)

As Built